Separating tramp oils from oil-in-water emulsions

ABSTRACT

Accumulations of tramp oils are removed from oil-in-water emulsions utilized as cleaners, lubricants and coolants by introducing into the emulsion a small but effective amount of a high molecular weight, water-soluble anionic polymer and heating the treated emulsion at an elevated temperature whereby the tramp oils are coalesced and floated to the surface of the emulsion. The essentially continuous but distinct tramp oil and emulsion phases are then readily separated.

United States Patent [1 1 Treat et a1.

1 1 SEPARATING TRAMP OILS FROM OIL-IN-WATER EMULSIONS [75] Inventors:Lyle G. Treat, Ferguson, Mo.;

Porter Hart, Lake Jackson, Tex.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: Mar. 31, 1972 [2]] Appl. No.: 239,939

Related U.S. Application Data [62] Division of Ser. No. 37,840, May 15,1970, Pat. No.

[52] U.S. Cl. 134/10, 134/40 [51] Int. Cl B08b 7/04 [58] Field of Search210/23, 43, 45, 60;

[56] References Cited UNITED STATES PATENTS 3,478,874 11/1969 McLean eta1 210/23 [451 Apr. 9, 1974 4/1967 Sackis 252/344 3,528,928 9/1970Rushton 252/344 X 3,479,283 1l/1969 Harrison 210/54 X 2,027,965 1/1936Dellmann 210/56 X 3,090,759 5/1963 Jenkins 252/344 3,409,551 11/1068Treat 252/336 3,634,243 l/l972 Wessel et a1 252/493 X Pllflltll)Emminer-Morris O. Wolk Assistant E.\'aminerArno1d Turk Attorney, Agent,or FirmEdward E. Schilling 5 7 ABSTRACT 2 Claims N0 Drawings SEPARATINGTRAMP OILS FROM OIL-IN-WATER EMULSIONS CROSS-REFERENCE TO RELATEDAPPLICATION This is a division of application Ser. No. 37,840 filed Mayl5, 1970, now US. Pat. No. 3,687,845.

The instant invention concerns a method for purifying oil-in-wateremulsions, such as are employed in the cleaning, lubricating and/orcooling of metal surfaces.

For instance, it is commonplace to utilize oil-in-water emulsions tolubricate and cool metals which are being fabricated as by rolling,drawing, cutting, milling, drilling and the like shaping operations. Theemulsion is usually sprayed onto the surface being worked and sometimesthe equipment utilized. It then drains off the workpiece or equipmentand is recovered for reuse.

Frequently, in the use of such emulsions, foreign oils and greasesaccumulate from hydraulic oils, bearing lubricants and protectivecoatings to introduce a substantial quantity of a foreign oil phase,otherwise referred to herein as tramp oil. Usually, but not necessarily,such oils are of a substantially greater viscosity than the oil of theemulsion phase. If allowed to remain in the emulsion, the foreign oilsresult in the loss of desirable lubricity and the discoloration orgrease staining of work pieces.

Separation of the tramp oils from the oil-in-water emulsion systems hasbeen difficult with prior technology and this often has meant earlydischarge and replacement of the system; a result which is bothexpensive in the cost of the new materials and in the cost of treatingthe waste for satisfactory ultimate disposal. In the latter regard, itis considered relatively difficult to remove the principal components ofthe oil-in-water emulsions, i.e. hydrocarbons and dispersants fromaqueous waste streams. Accordingly the discharge of v emulsionlubricants has sometimes meant a significant pollution problem.

It would be desirable, and it is a principal object of the instantinvention, to provide a new method for removing tramp oils fromoil-in-water emulsions utilized in the metal working, fabricating andcleaning arts.

A further object is to provide a method for simple flotation of trampoils without breaking the desired oil-inwater emulsion.

Still another object is to provide a direct and economical method forseparating tramp oils from metal working lubricants and coolants.

A still further object is to provide an improved process for lubricatinga metal rolling mill while minimizing lubricant waste discharge. i

In accordance with the instant invention, the forego ing-objects, andother benefits, as will become apparent hereinafter, are achieved bysubjecting an oil-in-water emulsion to a processing sequence whichcomprises the following steps. To an oil-in-water emulsion containing,as basic ingredients, a water-immiscible oil, an anionic or nonionicsurfactant and water and containing, as a foreign ingredient, a trampoil phase is added a small amount of a high molecular weight,water-soluble,'anionic polymer with sufficient agitation to disperse thepolymer throughout the emulsion. The emulsion isenergized, such as byheating at an elevated temperature sufficient to induce coagulation ofthe disperse tramp oil phase which then floats to the surface of theemulsion. Separation of the coalesced tramp oils is readily accomplishedas by skimming or withdrawing the un derflow emulsion. In a typicalindustrial process. susceptible to treatment by the method of thepresent invention, e.g., rolling or cleaning metal, the following stepsare practiced. The metal is contacted with an oilin-water emulsioncontaining water, a water-immiscible oil and an anionic surfactant. Thenthe emulsion is recovered and treated with a small amount of anappropriate water-soluble anionic polymer. Then the emulsion isenergized, and finally the emulsion is recycled into contact withadditional metal.

The polymer utilized in the instant invention is characterized by havingalong the polymer chain a plurality of carboxylate and/or sulfonategroups having the formulas COOM and SO M, respectively. In theseformulas, M is a water soluble cation, such as for example, an alkalimetal, ammonium, water soluble amine or hydrogen. By high molecularweight is meant the polymers are of flocculant grade, i.e. they arecapable of inducing the formation of flocs when added in smallconcentrations to aqueous suspensions of an oppositely charged dispersephase. A polymer has sufficient mo lecular weight for the purposes ofthe instant invention when a 0.5 per cent by weight solution thereof inwater at pH 4 and 25C. exhibits a Brookfield viscosity of at least about10 centipoises, preferably at least about centipoises.

In a preferred operation, addition of the polymer is followed by aperiod of mild or gentle agitation during which polymer is dispersedthroughout the system and agglomeration of disperse bodies of tramp oilis promoted. Normally, the emulsions will contain sufficient hardnessions and/or other metal ions to suitably condition the dispersed trampoils for reaction with the polymer. If not, a small amount of polyvalentmetal ion may be added so as .to impart the necessary hardness to theemulsion for efficient treatment with the polymers according to theinvention. Polyvalent metal ions that may be added for this purposeinclude the water soluble calcium, magnesium, aluminum and iron salts.From about 10 to 100 parts per million, based on the weight of the totalsystem, will usually be sufficient to condition the tramp oils forcoagulation.

Effective energy levels to promote coalescence and floating of thedispersed foreign oils will vary according to the nature andintrinsic'viscosities of these oils. Although the instant invention isnot predicted upon an explanation of any theory by which the inventionoperates, it is believed that the anionic polymer 'flocculates thedispersed foreign oils, which have not been stabilized in suspension byan anionic surfactant. This flocculation is promoted by the presence ofpolyvalent metal ions and any metal particles, which these oils may haveaccumulated from the environment of their use and from the aqueous phaseof the emulsion. Once coagulated, the energizing step, e.g. heating,promotes their coalescence as by reducing their surface tensionter-immiscible oils, anionic or nonionic surfactants and water. Typicalformulations are described by Treat in US. Pat. No. 3,409,551, beginningat column 2, lines 7 through column 3, line 25. In addition tothe aboveessential components, the emulsions will frequently of the oil.

contain additives for special effects, such as antifoaming agents,reducing agents, and stabilizers.

. Such emulsions will normally contain from about 80 to about 99 percent by weight water, as the external phase, in which there is dispersedfrom about 1 per cent to about 20 per cent, preferably from about 2 percent to about per cent by weight of an organic phase comprising awater-immiscible oil and an anionic surface active agent. The latterwill be employed in an amount from about 3 to about per cent, preferablyfrom about 5 to about 10 per cent, based on the weight Thewater-soluble, anionic polymers employedin the instant invention arecharacterized by substitution with a plurality'of carboxylate and/orsulfonate groups.

-Water-soluble as used herein means that the polymers solubilizinggroups ensures that the resulting polymer is properly water-soluble. Aminimum of about 4 mole percent of the monomer moieties combined in thetinished polymer should bearan anionic substituent to assure sufficientanionic properties. Preferred polymers are sulfonated polyvinylaromaticsof the benzene series, e.g. polystyrene and'polyvinyl toluene which beara plurality of sulfonate groups along the polymer backbone.

Other anionic polymers suitable for use in accordance with the inventionare the high molecular weight, water-soluble copolymers of styrene andmaleic acid. Such copolymers are generally employed in the form of thealkali metal salts thereof, preferably the sodium salt.

Anionic acrylic polymers that are useful in the present invention arewater-soluble, high molecular weight polymers obtained by thevinylpolymerization of acrylic acid, methacrylic acid, sulfoethyl acrylate,carboxyethyl .acrylate and water-soluble salts of the foregoing, or bycopolymerizationof theacidic monomers, or alkali metal salts thereof,with suitable amounts up to a majorproportion, e.g. 90 mole per cent orso, of other vinyl monomers such as acrylamide and methacrylamide.

Useful anionic polymeric agents can also be produced by hydrolysis ofpreformed nonionic polymers.

For'example, vinyl polymerized'forms of acrylonitrile ormethacrylonitrile can be hydrolyzed to convert the nitrile groups intothe corresponding alkali metal carboxylate groups. Similarly, polymersor copolymers of alkyl esters of unsaturated acids can be saponifiedwith an alkali metal hydroxide to convert ester groups to' alkali metalcarboxylate groups. v

In the practice of the invention, the emulsion is treated with a smallamount of the anionic polymer. Preferably from about 0.004 to about 0.01per cent by weight, and generally from about 0.001 to 0.1 based on theweight of the emulsion, induces effective flocculation of the dispersetramp oil phase. Although not necessary, it is preferred practice toadminister the polymer to the solution in the form of a dilute watersolution, usually containing from about 0.05 up to 0.5 per cent byweight dissolved polymer solids. Initial administration of the polymerto the emulsion is readily accomplished by thoroughly, and preferablyrapidly, mixing the polymer solution with the emulsion. This is usuallyaccomplished by rapid'a'nd vigorous agitation, as by stirring with apaddle agitator for a period within the range from 1 up to about 15seconds or so. Subsequently, the degree of agitation is reduced to avoiddestroying forming agglomerates of tramp oil. Because the polymer isanionic and the emulsion is stabilized with an anionic or nonionicemulsifier, there is essentially little or no interaction between it andthe emulsified oil phase. 1

Having carried out the addition of the polymer, the

emulsion is energized to promote coalescence of the agglomerated oilphase. Effective coalescence is readily ascertained simply bymaintaining an' aliquot of the emulsion under quiescent conditions andobserving whether oil globules float to the top or settle to the bottom,in the event the foreign oil is either sufficiently dense itself orsufficiently weighted with accumulated dense solids to sink in water.The energy input for this purpose is adequate when an essentiallycontinuous oil phase is induced. Such a phase may contain some entrainedwater and perhaps emulsion particles but its constituency will bevisibly distinct from that of the-adjacent emulsion layer.

Energizing techniques include the application of high frequency sound,radiant heat and radio frequency energy forms as well as simple directheating. When direct heating is used, some benefit of the invention willbe achieved by increasing the emulsion temperature by at least about10C, preferably 20C. Many'of the commercial oil-in water emulsionsutilized as lubricants and coolants for metal working are employed attemperatures within the range of 40 to 65C. Accordingly, treatmenttemperatures within the range from about 50 to about C. will besufficient to induce separation of flocculated tramp, oils. Essentiallyequivalent inputs from the other energy forms will produce similarcoalescence of the tramp oils.

Once the tramp oils have been coalesced into a dis tinct layer, they arereadily separated by conventional physical separatory techniques such asskimming, decantation or simply withdrawing the underflow emulsionliquid. A preferred skimmer is a revolving, Teflon resin coated drum,the lower edge of which is slightly immersed into the liquid body.

In a specific embodiment, oil-in-water emulsion containing 5 per cent ofa mineral oil emulsified with a pctroleum sulfonate was treated with acopolymer of acrylamide and sodium acrylate. Thepolymer had beenprepared by polymerizing acrylamide and hydrolyzing about 30 weight 'percent of the initially available carboxamide groups to sodium.carboxylate groups. The polymer had a 0.5 per cent water solutionBrookfield viscosity of about 2,000 centipoises, which corre- Sponded toa molecular weight of approximately 2 million. To each 1 liter ofemulsion was added 40 milliliters of a 0.1 per cent by weight solutionof the polymer. Dispersion of the polymer throughout the emulsion waspromoted by about 5 minutes of mild agitation with a laboratory paddlestirrer. The polymer addition increased the charge condition of thesystem from about 50 microamperes to 72 microamperes, as measured by aLeeds and Northrup I-Iydroscan meter. The latter instrument yields ameasurement which is a function of the zeta potential of the emulsionand is generally proportional to the magnitude and polarity of thecharge condition of the emulsion particles. The meaning of themeasurement is further described in US. Pat. No. 3,399,133.

The treated emulsion was then heated to about 60C. and maintained underquiescent conditions for about minutes. The tramp oils, including, i.e.,carrying some dispersed dirt, coalesced and rose to the top of theemulsion phase. The resulting film of oil was easily separated byskimming.

In subsequent operations, the treated emulsion was readily filteredthrough a diatomaceous earth coated filter to remove further impurities.

In a manner similar to the foregoing, the removal of tramp oils fromoil-in-water emulsions is promoted by the addition of flocculant gradesodium polystyrene crylamide-acrylate copolymers, acrylamide oxazoli-'done copolymers and sodium acrylate-pyrrolidone copolymers.

What is claimed is:

1. In a method of rolling or cleaning metal which comprises contactingthe metal with an oil-in-water emulsion, containing water, awater-immiscible oil and an anionic or nonionic surfactant, recoveringthe emulsion and recycling the same into contact with additional metal,the improvement which comprises introducing from about 0.001 to about0.1 per cent by weight based on the weight of the emulsion, of aflocculant-grade, water-soluble anionic polymer into the used emulsionwhich contains a contaminated tramp oil phase, said polymer beingfurther characterized as having along the polymer chain a plurality ofat least one of carboxylate and sulfonate groups having the formulasCOOM and SO M, respectively, wherein M is a water soluble cation andthen energizing the system to produce a temperature increase of at least10C. to promote coalescence of the tramp oil phase without breaking theoil-in-water emulsion, and separating any coalesced oil prior torecycle.

2. A method as in claim 1 wherein the water soluble cation is selectedfrom the group consisting of the cations of alkali metal, ammonium,amine, and hydrogen.

2. A method as in claim 1 wherein the water soluble cation is selectedfrom the group consisting of the cations of alkali metal, ammonium,amine, and hydrogen.